Spanning Tree Protocol (STP) is a link management protocol that can provide path redundancy while preventing loops in a network. For a conventional network, such as an Ethernet network, only one active path can exist between any two nodes for the network to function properly. If a loop were to form in the network, the amount of traffic that could be passed between infrastructure devices (e.g., switches, bridges, relays, among others) can quickly utilize the entire bandwidth available within each of the devices affected.
STP is compliant with IEEE 802.1D, entitled “Media Access Control (MAC) Bridges,” and which is incorporated herein by reference. STP can use a Spanning-Tree Algorithm (STA) to calculate an optimal loop-free path throughout a switched network by defining a tree with a root bridge and a loop-free path from the root to all infrastructure devices in the network. STP can force redundant data paths into a standby (blocked) state to create redundancy but not loops. If a network segment in the spanning tree fails and a redundant path exists, the STA can recalculate the spanning tree topology and activate the standby path. Infrastructure devices send and receive STP frames, called bridge protocol data units (BDPUs), at regular intervals. The devices do not forward these frames, but can use the frames to construct a loop-free path.
When two interfaces on a bridge are part of a loop, the STP port priority and path cost settings can determine which interface is put in the forwarding state and which is put in the blocking state. The port priority value can represent the location of an interface in the network topology and how well it is located to pass traffic. The STP path cost value can represent media speed.
The amount of computing resources utilized by STP, such as CPU, memory, and input/output (I/O), can be generally proportional to the product of the number of ports and the number of virtual LANs (VLANs) enabled on each port. With the proliferation of high port density switches (e.g., layer 2 (L2) and layer 3 (L3) switches) and Virtual Ethernet Port Aggregator (VEPA) devices that enable each switch front panel port to be virtualized into many more customer usable physical ports, new systems and approaches are required to optimize STP to keep a network operating system scalable and efficient.